This invention relates to a process for coloring wood and other cellulose based products. More specifically, the present invention relates to a method for imparting a desired color to wood products, which color will not fade or substantially change upon exposure to long term environmental weathering.
It has long been a primary goal of the wood treating industry to produce wood products that are artistically and aesthetically acceptable to the public, yet preserved from the destructive agencies of wood. Wood that is colored and preserved is in great demand for home use, especially for use in siding, fencing and decking. Unfortunately, many of the preservative solutions used to preserve against wood destroying organisms impart their own color to the wood. In many cases, the coloration imparted by these preservative solutions is undesirable for one reason or another.
Numerous conventional processes are available for coloring and staining wood, while several processes are available to preserve wood from the various wood destroying agencies. Many of these known processes are less than desirable because they are multi-step operations. Other conventional processes provide only a surface coloration which will scratch and wear away and require additional treatment or servicing for exposure to long term weathering.
One technique currently used to color wood is to paint the wood with an oil base paint or pigmented coating. Depending on the type of preservative used, some of the coatings will not adhere to the wood, resulting in blistering or flaking in a short period of time. Conventional organic preservatives, such as creosote and pentachlorophenol, pose problems because of oily films left on the treated wood, which require several months to season and even then it is difficult to paint or stain the wood.
Water-borne preservatives are preferred over the organic products because the wood is not coated with a film and can be readily painted or stained after treatment. However, here again, the coloration is only on the surface with these techniques, resulting in limited permanence to weathering.
Alternatively, the wood may be precoated with a coloring agent, such as an oil base or latex paint, followed by treatment with the wood preservative. Many of the oil base or latex paints will form a coating on the surface of the wood which reduces or eliminates the penetration of the preservative into the wood. In many cases, the coatings and the preservatives are incompatible.
In more recent years attempts have been made to develop processes which color and preserve the wood simultaneously. One such process is disclosed in U.S. Pat. No. 4,313,976. This process consists of using a specific naphthalene or benzene derivative compound having hydroxy, amino or sulfonic acid functional groups attached to a carbon ring. One of the drawbacks associated with this system is that it will weather from its original reddish brown color to a light brownish gray color after about six to twelve months exposure to the elements.
Therefore, due to the shortcomings associated with current methods for wood treatment, the need still remains for a process whereby wood may be colored and preserved in a single or combined operation. More particularly, the need remains for an improved process wherein the wood product resulting after treatment is able to withstand long term weathering without any substantial loss of color.